Air traffic volume is expected to triple in the U.S. and Europe by 2025, and as a result, the aerospace industry is facing stricter noise regulations. The engines and the airframe are the two principle sources of noise on an aircraft. One of the significant sources of airframe noise is the deployment of high-lift devices like a leading-edge slat which is heavily used in the vicinity of airports. The unsteady turbulent flow over a leading-edge slat is studied herein. In particular, Particle Image Velocimetry (PIV) measurements were performed on a scale-model wing equipped with a leading-edge slat in the H.J. Irving-J.C.C. Picot Wind Tunnel. Two Reynolds numbers based on wing chord were studied: Re = 6x10 5 and l.3x10 6 . PIV measurements of the mean flow, Reynolds stresses, turbulent kinetic energy, and vorticity, revealed that a distinct shear-layer forms at the slat cusp that appears to be more curved for the lower Reynolds number case. A snapshot Proper Orthogonal Decomposition (POD) analysis indicated that differences in the time-averaged statistics between the two Reynolds numbers were tied to differences in the coherent structures formed in the slat cove shear layer. In particular, the lower Reynolds number flow seemed to be dominated by a large-scale vortex formed in the slat cove that was related to the unsteady flapping and subsequent impingement of the shear-layer onto the underside of the slat. A train of smaller, more regular vortices was detected for the larger Reynolds number case which seemed to cause the shear-layer to be less curved and impinge closer to the tail of the slat than for the lower Reynolds number case. The impingement of the shear-layers on the slat and the main wing are expected to be significant acoustic sources.
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